There is a known arrangement in which a plurality of thread delivery devices, each delivering one thread, are distributed along the circumference of a support ring above a conventional circular knitting machine. Each thread delivery device in this case comprises a roller or pulley, all of which are driven by a common driving belt which in turn is driven by a driving wheel. With these known thread delivery devices, the thread to be drawn off each bobbin is passed between the driving belt and pulley at the point of contact thereof so that it is conveyed by the pulley or belt and can then be fed to a textile machine in the conventional manner. The running speed of the driving belt must be varied to enable the feeding speed of the thread delivery devices to be varied. In the case of the known arrangement this is done by altering the effective diameter of the driving wheel, the driving belt in each case being simultaneously maintained in a clamped position by a clamping device even when the driving wheel diameters are different. The diameter of the driving wheel can be varied with the aid of a plurality of separating members which are arranged between two pulleys and, together with the outer circumference thereof, form the running surface of the driving belt. The various separating members are radially slidable relative to the axle of the driving wheel so that the diameter of the running surface can be infinitely varied over a relatively wide area.
Since unavoidable slipping occurs both between the driving wheel and driving belt and between the pulleys associated with each thread delivery device, particularly when a great number of thread delivery devices are simultaneously driven by a single driving belt, such slipping altering the desired thread delivery speed in each respective case, the running surfaces of both the driving wheel and the various pulleys were provided with pins which engage in holes in the driving belt. This positive connection between the running surfaces of the driving wheel and pulleys, on the one hand, and the driving belt, on the other hand, reliably prevents slipping even when a very large number of thread delivery devices are driven by a single driving belt. With these thread delivery devices it is also customary for the thread awaiting delivery to be guided not directly between the pulley and driving belt, but via a thread drum mounted on the same axle as the pulley, in which case either the thread to be delivered is wound only once around the thread drum or alternatively the drum can also store a predetermined thread supply simultaneously when the thread is wound around it several times and appropriately drawn off.
If a positive connection in the form of pins and holes is provided between the driving belt and driving wheel to prevent slippage, the variation of driving wheel diameter provided for varying the rate of delivery in the known arrangement cannot be used since, in the event of radial displacement of the separating members forming the running surface, the mutual spacing between pins provided on the circumference of these separating members would naturally also be altered.
The problem for the invention is to provide a new thread delivery device in which, despite a positive connection provided between the driving belt and driving wheel with the aid of pins and holes, the driving belt speed can nevertheless be simply varied by varying the effective diameter of the driving wheel.
The problem is solved in accordance with the invention with a thread delivery device of the said type in that, for the use of a driving belt provided in a manner known per se with holes in which pins engage to produce a slip-free connection with a running surface cooperating with the driving belt, the running surface of the driving wheel is formed by a second driving belt with pins on its outer side which, while the belt rotates between the driving wheel and a guide or idler pulley, engage in the holes in the first driving belt.
Owing to the arrangement, surprisingly simple in appearance, of a second driving belt on the variable effective diameter of the driving wheel, the mutual spacing between the pins on the outer surface of this second belt can be kept constant irrespective of the size of the effective diameter. In this connection the second driving belt is maintained under constant tension with the aid of a guide pulley irrespective of the diameter of the driving wheel. The thread delivery device according to the invention therefore combines the advantages of simple adjustment of the driving belt speed through continuous variation of the effective diameter of the driving wheel and of a slip-free positive connection between the driving belt and at least the driving wheel by means of holes and pins. In addition to the running surface of the driving wheel, the surfaces of some or all of the pulleys in the thread delivery devices could obviously be provided with pins.
In accordance with a preferred embodiment of the invention the driving wheel comprises two cone-shaped pulleys arranged on a common axle and driving the driving belt between them, the distance between these pulleys being variable to vary the effective diameter of the driving wheel. This possibility of varying the effective diameter of a driving wheel or pulley, which is basically known in belt drives, represents a solution which is very simple in construction and particularly reliable in operation for varying the effective diameter of the driving wheel.
In accordance with a first embodiment of the invention the guide pulley is an idler pulley of constant diameter, whose bearing is preloaded in the direction away from the driving wheel. With the aid of this guide pulley the driving belt is maintained under constant tension irrespective of the diameter of the driving wheel since the bearing of the pulley endeavours to maintain the maximum spacing from the axis of rotation of the driving wheel e.g. with the aid of springs.
In accordance with a second embodiment of the invention the guiding pulley is an idler pulley comprising two cone-shaped or tapered wheels which are mounted on a common axle and the distance between which can be increased in opposition to the force of a spring in order to reduce the effective diameter of the idler pulley. In this case the pulley is therefore mounted in a similar manner to the driving wheel, the spring acting on one of the cone-shaped wheels causing the effective diameter of the idler pulley to be constantly varied in the opposite direction to the effective diameter of the driving wheel.
One of the cone-shaped pulleys of the driving wheel is axially rigidly secured on the axle while the other cone-shaped pulley can be fixed at a predetermined distance from the first cone-shaped pulley with the aid of a screw thread provided on the axle and an adjusting nut associated with the pulley. Through appropriate adjustment of the adjusting nut, a predetermined diameter of the driving wheel and therefore the desired driving belt speed in each case can be infinitely preselected.
In accordance with an embodiment of the invention the second driving belt is designed and/or made of such material that substantially no slipping occurs between the belt and driving wheel.